1. Technical Field of the Invention
The present invention relates generally to a vehicle control system designed to control exertion of braking force on wheels of a vehicle when being at a stop.
2. Background Art
Japanese Patent First Publication No. 2008-44443 discloses a vehicle control system equipped with a hill holder device working to prevent the vehicle from accidentally rolling backward when the driver starts the vehicle on steep hills. This system is designed to keep the hydraulic braking pressure at a high level to apply the braking force to wheels of the vehicle when three conditions are all met: an inclination of the road surface is greater than a given value, the brake pedal of the vehicle is being depressed, and the speed of the vehicle is zero (0), and then continues to keep the hydraulic braking pressure after the driver releases the brake pedal to avoid the backward rolling of the vehicle when the drive starts the vehicle.
Most of vehicle speed sensors have a dead zone where a measured value of speed of the vehicle shows zero (0) around a zero real speed of the vehicle. The above vehicle control system may, therefore, encounter the problem that the speed of the vehicle is determined to be zero in error when the vehicle is braked while being running on the slope, so that the real speed of the vehicle drops, thus causing the hill holder device to exert a great braking force on the wheels, leading to sudden deceleration of the vehicle not expected by the driver.
The above problem is usually faced by systems equipped with no hill holder devices, but designed to apply the braking force to the wheels of the vehicle at rest.